This invention relates to a machine for forming cylindrical bales of crop and more particularly relates to such a machine for making bales which are of low density or "soft".
Machines, towed by a tractor, for forming large cylindrical bales of hay (so-called "round balers") are well known. As the machine advances, the crop is removed from a windrow by a pick-up mechanism and delivered rearwardly to a baling chamber where it is rolled round upon itself into a bale.
In one form of such a machine, the baling chamber is defined by runs of belts which move outwardly to enlarge the chamber so as to accommodate the bale as it grows in size. The belts are trained over rolls connected to a drive. A pair of rolls is located at the top of the chamber and these rolls are carried by a swingable tension arm on either side of the machine enabling the two rolls to swing upwardly as the girth of the bale increases. The tension arms are connected to hydraulic piston and cylinder units, i.e., tension cylinders, which resist their upward movement sufficiently to ensure that a dense bale is formed. Hydraulic piston and cylinder units are used to raise a rear gate of the machine to release a completed bale and these units, i. e., gate cylinders, are connected to the tension cylinders.
In most circumstances, a uniformly dense bale is highly desirable. However, in some conditions, it is useful for the core (or indeed the entire bale) to be of low density or soft. Such conditions occur, for example, when the crop has to be baled wet, and hot air is subsequently blown through the completed bale to reduce the excess moisture. This treatment is obviously more effective with a looser bale. Certain special applications also make a softer bale more desirable, e.g., a machine for grinding straw prior to its use in mushroom growing beds will more readily accept this type of bale.
The hydraulic circuitry involving the tension cylinders which brake the tension arms as referred to above includes first and second supply/return lines from quick couplers, connected to the hydraulic supply of the tractor towing the baler, to the rod ends and piston ends respectively of the cylinders. Pressure in the rod ends resists extension of the cylinders and therefore affords the braking effect on the tension arms. Thus, control of this pressure provides control of the density of the bale.
In the known Model 550 Round Baler, produced and marketed by Deere & Company, the pressure is controlled as follows. A check valve is disposed in the first supply/return line running from one of the couplers to the rod ends, and allows flow in the direction of the rod ends. The rod and piston ends are connected by a bypass line interconnecting the first and second supply/return lines which respectively run to the rod and piston ends, with the bypass line being connected to the first supply/return line at a point downstream of the check valve. Located in the bypass line is an adjustable bale density relief valve. The setting for the opening of this latter valve, typically at 180 bars, determines the pressure at which the rod ends are relieved and hence the density of the bale being formed. U.S. Pat. No. 4,391,187 granted to Koning et al. on 5 July 1983 discloses and describes a tensioning system substantially similar to that embodied in the Model 550 Round Baler.
It is desirable to be able to minimize the pressure in the rod ends to produce softer bales (or cores) when needed, and yet maintain the capability of the machine to make dense bales. A simple way of achieving this has been proposed in which a valve is disposed in a line between the rod and piston ends of the tension cylinders and is selectively shiftable between an open position connecting the opposite ends of the tension cylinders to each other for effecting formation of a bale having a soft core and a closed position enabling pressure to be maintained in the rod ends for dense baling. However, the hydraulic circuitry connecting the tension cylinders and gate cylinders is such in, for example, the afore-mentioned Model 550 Round Baler (as will be explained later in detail) that, after closing the gate following release of a completed bale through the raised gate, hydraulic fluid is trapped under pressure in the rod ends of the tension and gate cylinders. This fluid flows to the piston ends to equalize the pressure at the rod and piston ends, but nevertheless, due to difference in surface areas at the ends, the gate cylinders tend toward unwanted creeping extension and thereby release latches which keep the gate closed with the result that baling cannot start until the latches have again been secured.